(1) Field of the Invention
The present invention relates to a solid-state imaging device, and especially to a structure of a sensor in a MOS-type solid-state imaging device.
(2) Related Art
A MOS-type solid-state imaging device which is used as an imaging device, such as a digital still camera, includes a sensor composed of a plurality of pixels arranged two-dimensionally (arranged in a matrix, for example) (Japanese Published Patent Application No. 2004-186407, Japanese Published Patent Application No. 2002-335455, and U.S. Pat. No. 6,838,715). The following describes a structure of a sensor in a conventional MOS-type solid-state imaging device, with reference to FIG. 1.
As shown in FIG. 1, a pixel 900 in the MOS-type solid-state imaging device includes a photodiode 9001 and three transistors (a transfer transistor 9002, an amplifying transistor 9004, and a reset transistor 9005). The photodiode 9001 is an element which converts received light into a charge corresponding to an intensity of the received light, and accumulates the converted charge. Also, one end of the photodiode 9001 is connected to a source of the transfer transistor 9002. On a drain side of the transfer transistor 9002, a floating diffusion (hereinafter, referred to as “FD”) 9003 which receives a transferred charge is formed. The FD 9003 and the amplifying transistor 9004 are connected via a charge transfer line 9008.
Drains of the amplifying transistor 9004 and the reset transistor 9005 are connected to a power supply line 9006 that is extended in a Y-axis direction in FIG. 1, and a source of the amplifying transistor 9004 is connected to a vertical signal line 9007 that is extended in the Y-axis direction same as the power supply line 9006. After the transfer transistor 9002 is ON, the charge generated in the photoelectric conversion by the photodiode 9001 is transferred to the FD 9003. Also, after the signal charge is inputted to the gate of the amplifying transistor 9004, the amplified signal is outputted to the vertical signal line 9007.
The pixel 900 in the sensor has the above-mentioned structure. The following describes a layout of the charge transfer line 9008, the power supply line 9006, and the vertical signal line 9007 in the pixel 900, with reference to FIG. 2. Note that in FIG. 2, a plurality of pixels are expressed in pixels 901 to 904 by dividing them into forming areas of a sensor 90. However, each of the plurality of pixels 901 to 904 has a same structure as the pixel 900 with regard to a circuit.
As shown in FIG. 2, in the pixels 901 to 904, charge transfer lines 9018 to 9048 and vertical signal lines 9017 to 9047 are formed at the same height level in a thickness direction of the device. Also, power supply lines 9016 to 9046 are formed in an upper layer than the charge transfer lines 9018 to 9048 and the vertical signal lines 9017 to 9047. Moreover, in the pixels 901 to 904, each of centers L901 to L904 of the power supply lines 9016 to 9046 that are formed in the upper layer is in a shifted position located toward a center L9 of the sensor 90, in accordance with each arrangement with respect to the center L9 of the sensor 90 (which is referred to as so-called “shrink”). These shift arrangements of the power supply lines 9016 to 9046 are intended for an improvement in an oblique-incidence characteristic of incident light.
However, in the conventional MOS-type solid-state imaging device in which the power supply lines 9016 to 9046 are arranged in the shifted positions located toward the center L9 of the sensor 90 as shown in FIG. 2, output signals in the pixels 901 to 904 vary, causing uneven brightness of an output image, i.e. so-called shading occurs. In detail, in the structure in which the power supply lines 9016 to 9046 are arranged in the shifted positions located toward the center L9 of the sensor 90 by shrink as shown in FIG. 2, the pixels 901 and 902 that are located on a left side in a X-axis direction differ from the pixels 903 and 904 that are located on a right side in the X-axis direction in the following respect. That is, distances between the power supply lines 9016, 9026 and the charge transfer lines 9018, 9028 are different from distances between the power supply lines 9036, 9046 and the charge transfer lines 9038, 9048. This causes a difference between parasitic capacitances C9011 to C9041 in the pixels 901 to 904.
The parasitic capacitances C9011 to C9041 in the pixels 901 to 904 are location elements which compose a capacitance of the FD 9003, and the variations between the parasitic capacitances C9011 to C9041 cause a difference of output signals when same number of electrons are generated in photodiodes 9011 to 9041.